upstream-tls-verify: Verified TLS to an inbound domain's upstream

Owner, 2026-10-18: "Оба предложения делаем"; the mockup is c10cd78. The
security audit's M7: Required is Postfix's encrypt level, which checks no
certificate - it keeps the mail from a listener, not from one who answers
in the upstream's place.

- A fourth TLS mode, Verified, stored as Postfix's level secure (migration
  0014 rebuilds inbound_transports with the wider CHECK; schema 14) and
  written to the TLS policy map like the others. Postfix matches the
  certificate against the next hop's name (smtp_tls_secure_cert_match =
  nexthop, dot-nexthop, the default; postconf(5)), so Verified is refused
  for an upstream given by address (checkSecureHost).
- Postfix's SMTP client trusts Debian's ca-certificates bundle
  (smtp_tls_CAfile): Postfix trusts none by default (DEF_SMTP_TLS_CA_FILE
  "", DEF_TLS_APPEND_DEF_CA 0). The levels may and encrypt only log the
  verdict, so mail to recipients' MX is unchanged.
- The page: the select's fourth option, a help line under it, the lead
  "over verified TLS", the list's tag "verified"; Help word for word with
  the mockup; guide § Inbound relay, with a posttls-finger command to try
  an upstream first.

Tests: TestVerifiedTLSNeedsTheUpstreamsName, TestRenderInboundMapsSecure,
TestUpstreamTLSModeSecure; schema tests at 14. e2e
inbound_upstream_verified_tls: an address refused, a name saved as
"[sink]:25 secure" in tls_policy, the page says verified, the CA file set
and present, and posttls-finger -l secure with it calls the stand's
self-signed port 25 "Untrusted" (the stand has no TLS upstream). make e2e
(65 passed) and go vet + go test (26 packages) on the test server for this
tree. Tried against the live upstream from the 2.14.5 container:
mc-ent.mixfed.ru gives "Verified TLS connection established".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/postfix/inbound_test.go

@@ -136,3 +136,18 @@ func TestRenderInboundMapsOneTLSLinePerNextHop(t *testing.T) {
 		t.Errorf("tls_policy = %q, want the next hop once", tlsPolicy)
 	}
 }
+
+// Verified TLS is Postfix's secure level, written as the others are; the
+// certificate is matched against the next hop's name by the main.cf default
+// (smtp_tls_secure_cert_match = nexthop, dot-nexthop).
+func TestRenderInboundMapsSecure(t *testing.T) {
+	_, _, _, tlsPolicy, err := renderInboundMaps([]InboundRoute{
+		{Domain: "in.example.com", Host: "mx.example.net", Port: 25, TLSMode: "secure", RecipientMode: "any"},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(tlsPolicy) != "[mx.example.net]:25 secure\n" {
+		t.Errorf("tls_policy = %q", tlsPolicy)
+	}
+}